1. Field of the Invention
The invention relates to a misfire detection apparatus and a misfire detection method for an internal combustion engine.
2. Description of the Related Art
Recently, a hybrid vehicle has been widely used as an environmentally-friendly vehicle. In the hybrid vehicle, a direct-current power supply, an inverter, and a motor driven by the inverter are used as power sources, in addition to an internal combustion engine.
For example, Japanese Patent Application Publication No. 2001-65402 (JP-A-2001-65402) describes a control apparatus for a hybrid vehicle, which is a misfire detection apparatus for an internal combustion engine provided in such a hybrid vehicle. The control apparatus accurately detects a misfire even when a vibration suppression control is executed, and controls an engine so that the engine continues to appropriately operate. The control apparatus for a hybrid vehicle is applied to a hybrid vehicle that travels using at least one of the engine and a motor as a power source. When the engine operates, the control apparatus executes the vibration suppression control to suppress variation of torque of the engine using the motor or a generator connected to the output shaft of the engine. The control apparatus includes torque correction amount calculation means for calculating a torque correction amount for the motor or the generator, which is used to suppress the variation of the torque of the engine, when the vibration suppression control is executed; and misfire detection means for detecting a misfire in the engine based on the torque correction amount for the motor or the generator.
In the control apparatus for a hybrid vehicle described in the above publication, a misfire in the engine is detected based on the torque correction amount for the motor or the generator when the vibration suppression control is executed. Thus, it is possible to accurately detect a misfire, and to control the engine so that the engine continues to appropriately operate.
A transmission mechanism, which is provided between an internal combustion engine and drive wheels, may be provided with a damper that reduces torsion of a rotational shaft. In a hybrid vehicle that includes the damper, if a single misfire occurs in the internal combustion engine, the rotational speed of the rotational shaft of the internal combustion engine changes to a small extent, and thus, the accuracy of detecting a misfire decreases for the following reason. If a single misfire occurs in the internal combustion engine, the spring force of the damper resists a force that decreases the rotational speed of the rotational shaft of the internal combustion engine. This suppresses a decrease in the rotational speed of the rotational shaft of the internal combustion engine, thereby decreasing the accuracy of detecting the characteristic change in the rotational speed, which is caused by a misfire.
However, in the above-described publication, consideration is not given to the decrease in the accuracy of detecting a misfire. Thus, the accuracy of detecting a misfire needs to be improved.